WRT54G drops wireless connection at fast speeds

I just installed wireless Linksys router WRT54G. Everything works fine, browsing, email etc. that is until I launch bittorent (Bitcomet to be precise) and the download speed reaches 200-300 K/s (the router is connected to a cable modem). Once this happens, router randomly drops wireless connection every 5-10 minutes. I upgraded to the latest official firmware, tried to play with MTU settings (lowered it gradually from 1500 to 1400) changed channels - to no avail. Any help is appreciated.